The present invention relates to a device for engaging and disengaging rollers, comprising pairs of upper and lower horizontal rollers. The rollers convey sheet-like materials and squeeze off any residual liquid adhering to the sheet-like materials. A bearing which can be raised and lowered with respect to the lower roller, is provided at the axial ends of each upper roller.
A device of this kind has been disclosed by German Offenlegungsschrift No. 2,326,122, in which each shaft journal of a pair of upper and lower rollers extends into a housing on each side. In this arrangement, the lower bearing is fixed, whereas the upper bearing is free to pivot on a pin arranged eccentrically relative to the axis of the upper bearing. The side of the bearing opposite to the pin is connected with a joint. The joint, in turn, is hinged to the lower end of a lever which is adapted to swivel about a horizontal pin mounted in a bracket attached to the upper wall of the housing. An actuating handle projecting from the top of the housing is connected with the swivelling lever. The lever and the joint constitute a toggle lever arrangement which forces the upper rollers against the lower rollers when the arrangement is in the extended position, and which raises the upper rollers from the lower rollers when the actuating handle is shifted. A relief spring ensures that the upper rollers are arrested in the raised position.
Each end of each upper roller is provided with a separate actuating lever. It is therefore necessary, using this device, to actuate quite a number of handles to raise the upper rollers. Raising the rollers is required prior to any prolonged standstill, for example, overnight or for the weekend, in order to prevent the upper rollers from sticking to the lower rollers. This is a time-consuming operation, so that the operator is tempted to omit it at times. If, however, the rollers are left pressed together, the rollers may stick together, as described above, and, moreover, deformations of their surfaces may occur. Such deformations may jeopardize a safe and gentle transport of the sheet-like materials, in particular of printing plates, and a complete squeezing off of liquid from the sheet-like materials particularly in horizontal processing equipment.
In order to facilitate the operation of a developing device for printing plates, European Pat. No. 0,004,337 (equivalent to U.S. Pat. No. 4,206,527) proposes a device, in which a pivoting fork head having an upper and a lower arm is provided for engaging the bearings of the upper rollers. The pivoting axis of the fork head extends parallel to the direction of transport of the printing plates. The bearings are actuated via a toggle lever arrangement, whereby the upper arm of the pivoting fork head exerts pressure on the top of the bearing when the bearing is in a lowered position, and the lower arm of the fork head supports the bearing in a raised position. A first end of each toggle lever arrangement is connected with the fork head. A second end of each toggle lever arrangement is connected with a rotatable control shaft which is common to all toggle lever arrangements, and supported parallel to the direction of transport of the printing plates. It is true that in employing this device it is possible to raise and to lower all upper rollers by one single lever actuation, but the construction of the toggle lever arrangement and the forked heads equipped with two arms is complicated and expensive.
There has also been disclosed an apparatus for developing printing plates, which comprises rollers which are arranged in pairs and the ends of which are supported in side plates. These side plates are divided into upper and lower parts, and the upper part of each side plate is pivoted and equipped with the corresponding lifting elements in such a manner that the complete upper parts of the side plates or the upper part of the processing station, respectively, may be lifted together with all upper rollers.
This latter apparatus is also comparatively expensive, particularly if the effort which must be exerted by the operator for the lifting operation is to be kept moderate. In addition, the above arrangement cannot be used in an installation including a number of component processing stations which may be assembled, in a modular manner, with other structural units to form the complete installation.